The objectives of the proposed research project are as follows: 1) Define the terminal complement components (C5, C6, C7, C8, C9) or complex (C5b-9) antigenic and/or hemolytic activities associated with the outer membrane surface of human peripheral blood lymphocytes or lymphoblastoid cells prepared or incubated in a variety of ways, e.g., lymphocytes will be prepared from defibrinated, EDTA, citrate or heparinized blood and incubated in autologous proteins. 2) The lymphocyte subpopulations expressing these antigenic and/or hemolytic activities will be determined. 3) The mechanism by which these terminal components or complexes become bound to the lymphocyte membrane will be investigated. 4) The effect of terminal complement component or complex binding on lymphocyte osmotic balance, viability and metabolism will be determined. 5) The functional role of these terminal complement components or complexes in lymphocyte mediated antibody-dependent or antibody-independent cytotoxic reactions, mitogenic responses and mixed lymphocyte reactions will be investigated. 6) The antigenic and physicochemical properties of lymphocyte-bound terminal complement components or complexes will be characterized. 7) The existence of lymphocyte receptors specific for terminal complement components or complexes will be determined and quantitated. The methods and techniques to be employed will include direct and indirect immunofluorescence using specifically purified IgG molecules of F(ab'2) fragments; specific microcomplement hemolytic molecular titrations; gel filtration and sucrose gradient ultracentrifugation to determine diffusion and sedimentation coefficients for lymphocyte-associated components and/or complexes as well as specific inhibition of hemolytic activities by IgG molecules prepared from monospecific antisera; many of the terminal complement components will be isolated by immunoaffinity column chromatography, radioiodinated by the lactoperoxidase procedure and used to quantitate specific lymphocyte membrane receptors; and lymphocytes and lymphocyte subpopulations will be prepared and characterized by standard procedures.